To make things even more difficult, many of the descriptions included spelling mistakes, were redacted for privacy reasons, or were simply left blank.Step one was making the documents easier to analyse.

The documents were provided to The Courier in a format that was unsearchable, so we were unable to check regular transactions or add up the total spend.

To get around this, the files had to be digitised using "optical character recognition" software: a program that reads documents and then produces an editable final copy.

While the software used for this process is one of the most powerful on the market, it isn't perfect, meaning we cannot guarantee what it produced is 100 per cent accurate.

However, because it would take many months to go through each transaction one by one, this method was chosen as the best way forward.

To double check what results the software produced, 100 random transactions were selected from the digitised database and compared to the original source documents.

The results from this test produced just one purchase amount error and a total of ten letters spelt wrong across seven transaction descriptions.

After the documents were digitised, we then conducted a number of searches to group together all the similar transactions made by council staff using purchase cards.

Because there appears to be no standardised form of explaining transactions, not all transactions grouped together can be considered equal.